Mass transfer characteristics in an axisymmetric wavy-walled tube for pulsatile flow with backward flow

Under the pulsatile flow with backward flow (PFBF) conditions, flow mixing and mass transfer characteristics are experimentally investigated in an axisymmetric wavy-walled tube at a net flow Reynolds number from 50 to 1,000. An electrochemical technique is employed to measure the mass transfer rate. An optimal Strouhal number corresponding to the peak value of the mass transfer enhancement factor is observed, which is independent of the oscillatory fraction of the flow rate, but decreases with the increasing net flow Reynolds number. It was found that the mass transfer enhancement under PFBF has the similar characters of resonant enhancement in two-dimensional (2-D) channels, but there also exists an essential difference since no self-sustained oscillation occurs in the wavy-walled tube.